An ethylene-tetrafluoroethylene copolymer (ETFE) is excellent in non-tackiness, pollution resistance, transparency, chemical resistance, weather resistance and heat resistance, and thus, is widely employed for various applications. For example, for a wall paper or a surface material of kitchen door, a composite sheet is employed, which is formed by laminating an ETFE film with a thermoplastic plastic sheet such as a vinyl chloride resin sheet or a polyethylene sheet or a thermosetting polyester sheet via an adhesive agent. For a surface material of a gas range hood or a kitchen wall panel, a material produced by laminating a painted metal plate with an ETFE film via an adhesive agent, is employed. Further, a tube made of an ETFE covered with a rubber, an urethane resin, a nylon resin etc. via an adhesive agent, is employed as a tube for fuel, excellent in barrier property against gasoline and durability.
In particular, in recent years, weather resistance of ETFE draws an attention, and instead of glasses, ETFE films are used as surface materials of flexible solar cells. Such an ETFE film employed as a surface member of a solar cell is thermally laminated at a temperature of from 135 to 160° C. with a material such as an ethylene-vinyl acetate copolymer (EVA), a modified polyethylene or a polybutylvinylal (PVB) that are materials for wrapping a solar cell, without using an adhesive agent.
When an ETFE molded body is adhered to e.g. a plastic sheet or a metal plate to form a laminate and when a surface of the molded body is printed with a printing ink, the molded body is applied with a surface treatment in order to improve adhesion to other members or other components.
As such a surface treatment to a fluororesin molded body, for example, a treatment using a corona discharge in the air is described in Patent Documents 1 and 2. However, by the surface treatment using a corona discharge, it is difficult to sufficiently improve the adhesion of the ETFE molded body to other materials or other components. Further, even if the adhesion of the ETFE molded body is improved just after the treatment, the adhesion cannot be maintained for a long time.
Meanwhile, Patent Document 3 shows a method of applying a surface treatment to a polyethylene terephthalate (PET) film by using a glow discharge produced by a pulsed electric field under predetermined conditions. Further, Patent Document 4 shows a method of applying a surface treatment to a polytetrafluoroethylene (PTFE) film by using a glow discharge produced by a pulsed electric field under predetermined conditions. However, even by applying the surface treatment described in Patent Document 3 or 4, it has been difficult to improve the adhesion of an ETFE molded body to other members and to maintain the adhesion for a long time.